Can a streamlined ship go underwater ?

[phavoc]

Here's the problem. Starships that have no inherent ability to counteract gravity would never be able to land and operate near cities - especially the futurisitic cities with 110+ floor buildings adjacent to (and surrounding) a starport.

They can: the Starship Operators Manual, Vol. 1 explains this in detail. I believe it is canon. Explicitly ships do not have anti-gravity drive in MT.

That is a reasonable assumption to make.

I have noticed that many want to make that assumption, and you can of course do as you wish in your game. It is not necessary for Traveller to work.

I believe MgT2 avoids these details to allow players to play as they wish which is why I noted that it is you can assume it or not:

You can of course assume whatever you want in YTU; I don't assume that spacecraft automatically have anti-grav drives unless they install a specific anti-grav drive.

Anti-gravity does in fact equal contra-gravity. How? By the definition of the words.

They are two different technical systems with different functional details, even if the names are similar.

None of this is made any easier with the jumble of rule sets and the inconsistency across them. Though I suppose it does make for some interesting forum fodder.

All of this is clearly defined in editions that care about detail, e.g. MT, TNE, and T5.

I believe we can settle the argument about whether or not Traveller ships have antigrav/contragrav lifters (you may dispute the definitions further but that's for another thread). You mad a statement about assumptions and a "YTU". I recently received my copy of Flatlined. Since this is an official MGT publication, the statement given in it makes it canon. On pg 8 there is a description of a craft, "the pilot managed to use residual energy in the ships lifters..." Checking the ship stats there is no mention of any special function or feature other than the standard M-drive that is on every ship profile.

So it would seem that without another mention of ships that specifically preclude the installation of a antigrav/contragrav lifters, that the default would be ships capable of landing on a world do, in fact, have them.

I am still interested in how you define antigrav and contragrav to be different systems. Which rule set are you pulling this from?

[Condottiere]

My feeling is that we've accepted the thrust vectoring aspect of gravitational based drives.

But in the hovering aspect, it would be a case of diminishing returns, in comparison with actual anti-gravity lifters.

[AnotherDilbert]

I am still interested in how you define antigrav and contragrav to be different systems. Which rule set are you pulling this from?

Anti-grav is defined in MT and T5, used in CT and MgT.
Contra-grav is defined in TNE.

As already stated in this thread: Anti-grav drives provides lift and propulsion (like a helicopter), contra-grav drives negates most gravitational pull but does not provide thrust for propulsion (like a hot-air ballon).

On pg 8 there is a description of a craft, "the pilot managed to use residual energy in the ships lifters..."

We can trade quotes all day long, it is not clearly defined in MgT.

This hints that spacecraft does not have anti-grav drives as standard.

A streamlined ship is designed to enter a planetary atmosphere, and can function like a conventional aircraft.
...
Partial streamlining allows a ship to skim gas giants and enter Atmosphere codes of 3 or less, acting in the same way as streamlined ships. In other atmospheres, the ship will be ponderous and unresponsive, reliant on its thrusters to keep it aloft.

I would rate the core rules above a fluff statement in an adventure, but that is just me, you can assume anything you like...

[phavoc]

Well, we had this same conversation 2 yrs ago (viewtopic.php?f=89&t=119461) and it wasn't settled then. The odds of it settling now aren't any better with age. We can call the devices whatever (contragrav, antigrav, lifters, oatmeal cookies, etc). The idea doesn't change, just the definitions between the many settings and publishers of Traveller.

Plus I don't think anyone is going to budge, so there's not point in continuing the thread.

[phavoc]

As an aside, for those of us who read Space Vikings (and for whom the Sword Worlders are named), I found an interesting blog post talking about size comparisons - the Space Viking ships of old were MASSIVE when compared to most Traveller starships. The Nemesis would be about a 2 million DT ship in Travller. There are some interesting size comparisons at the blog for those who like that sort of thing - http://www.enderra.com/2011/10/14/starsship-sizes/

[Condottiere]

Machinery may operate under the same principles, but some may be more efficient or specialized to function in a specific way.

[steve98052]

At least one classic book mentions System Defense Boats hiding in deep oceans when so outmatched by invaders that fighting would be suicidal. So at least some ships are built for "deep" underwater operations.

Per the quote below, it looks like underwater capability is routine at TL13. Given that purpose-built submarines predated space flight by nearly a century, we can assume that it's possible to add underwater capabilities to a starship well before TL13, but that it's an add-on feature, not standard practice. And it's an add-on feature used by System Defense Boats.

. . .
TL 13 . . . Advances in hull design and
thruster plates means that spacecraft can easily go
underwater. . . .

[steve98052]

I stumbled across how this works under GURPS Traveller rules, and although it's not directly applicable to Mongoose rules, it's not a bad starting point for a house rule. (As previously discussed, there's no need for house rules at TL13 and above, because the rules already allow them to maneuver underwater.)

So, what is the rule there?

. . . In GURPS Traveller, ships with vectored reactionless thrusters capable of more than 2 G of thrust, very good or better streamlining . . ., and total compartmentalization . . . are assumed to have the equivalent of a submersible hull. A submersible hull is required for most underwater operations, but ships without one may still be able to function in this environment.
. . .
To calculate Maximum Speed underwater (uSpeed), first determine:
Hydrodynamic Drag = 944 × cube root of (Total Displacement × Total Displacement).
Then:
uSpeed in MPH = 76 × cube root (Thrust/Drag). Total Displacement is in dtons and Thrust is in stons.
Crush depth in yards is 10 plus the DR of the hull or turrets (whichever is lower), multiplied by . . . 6 for [normal frames]. Divide this final result by the size modifier of the ship . . . If the ship does not have a submersible hull or the equivalent, divide again by 2.
. . .
Total Compartmentalization (adds 20% of hull mass to total weight). . . . costs MCr0.01 per ton of weight added.

For reference: 100 DR is the standard armor to protect a space vehicle from normal micrometeoroid impacts; a Scout ship has 200 DR. The size modifier is +8 at 100 dtons, and increases by 2 for every 10× larger, or by 1 for 3× larger (and divides similarly for smaller). A 100 dton hull has a mass 10 tons, an 800 dton hull has a mass of 40 tons, and an increase of 8× in dtons means an increase of 4× in tons, 2× dtons is 1.6× tons, 4× dtons is 2.5× tons, etc. A Scout ship has 800 thrust, worth about 2.1 G.

So, if we want to build a 100 dton starship-submarine according to these really complicated rules:
The base hull mass is 10 tons, so total compartmentalization adds 2 tons, and thus MCr0.02 (or just Cr20000)
Hydrodynamic drag = 944 × cube root of (100 × 100) = 20338
Underwater speed = 76 × cube root of (800 / 20338) mph = 26 mph = 41.6 km/h
Crush depth = (10 + 200) × 6) / 8 = 280 yards (or 140 yards without the added Cr20000 for total compartmentalization, which the standard Scout ship doesn't have) = 256 meters (or 128 meters)

Without showing my work:

Beowulf or Empress Marava, 200 dtons, DR 100, 640 thrust, standard compartmentalization
33284 drag, 14 mph or 22 km/h, crush depth 82 yards or 75 meters

Dragon system defense boat, 400 dtons, DR 1011, 11360 thrust, and heavy (not total) compartmentalization
51248 drag, 17 mph or 27 km/h, crush depth 340 yards or 311 meters

- - -

So, to put that in terms of a Mongoose house rule, a reasonable rule is 100 meters per armor point, but at least 50 meters, but maneuver is slower than a fish. At TL13 and above, double the depth limits, and maneuver is faster than a fish.

[Condottiere]

NASA’s Crazy Plan to Send a Space Submarine to Titan

https://www.youtube.com/watch?v=UYusz-MIJ4c